Two thin lenses of powers 12 D and -2D respectively are placed in contact, the power focal length and nature respectively will be:

Question

Two thin lenses of powers 12 D and -2D respectively are placed in contact, the power focal length and nature respectively will be: (A) 8 D, 0.8 m, convex (B) 14 D, 0.5 m convex (C) 5 D, 0.2 m, convex (D) 10 D, 0.1 m, convex

Tardigrade Admin · Accepted Answer

Given: P1=12 D, P2=-2 D Power of combination P=P1+P2=12-2=10 D Focal length f=(1/P)=(1/10) m =0.1 m The combined lens will be convex (convergent)

Q. Two thin lenses of powers $12 D$ and $- 2 D$ respectively are placed in contact, the power focal length and nature respectively will be:

8 D, 0.8 m, convex

14 D, 0.5 m convex

5 D, 0.2 m, convex

10 D, 0.1 m, convex

Given : $P_{1} = 12 D, P_{2} = - 2 D$
Power of combination
$P = P_{1} + P_{2} = 12 - 2 = 10 D$
Focal length $f = \frac{1}{P} = \frac{1}{10} m = 0.1 m$
The combined lens will be convex (convergent)

Q. Two thin lenses of powers 12D and −2D respectively are placed in contact, the power focal length and nature respectively will be: